When edit user email address, and input the incorrect email address,
there are two kinds of error message:
1.Input .@ab.ab, there is error message:
Invalid email address
2.Input firstname.lastname@example.org, there is error message:
Please provide valid email address.
It is not reasonable when email address passed front-end validation,
but failed back-end validation.
So front-end and back-end email address regular expression should be the same,
and add hint message for user to fill email address.